Method of forming conductive pattern, wiring substrate, electronic device and electronic equipment

ABSTRACT

A method of forming a conductive pattern having superior conductivity and better adhesion with a substrate is provided, thereby enabling a thick conductive pattern to be formed. The method comprises the steps of preparing a substrate, forming a metallic core containing metallic particles on the substrate by a droplet ejecting method so that the metallic core has a pattern substantially the same as the predetermined conductive pattern, and forming a plating layer so as to cover the surface of the metallic core by carrying out at least one electroless plating to thereby obtain the conductive pattern. A wiring substrate having the conductive pattern formed by the method, an electronic device provided with the wiring substrate and electronic equipment provided with the electronic device are also provided.

CROSS-REFERENCE

The entire disclosure of Japanese Patent Application No. 2004-311589 filed on Oct. 26, 2004 is expressly incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of forming a conductive pattern, a wiring substrate, an electronic device and electronic equipment, and more specifically relates to a method of forming a predetermined conductive pattern, a wiring substrate on which the conductive pattern is formed, an electronic device provided with the wiring substrate and electronic equipment provided with the electronic device.

2. Description of the Related Art

As a method of forming a conductive pattern (wiring pattern), there are know an electroless plating method and a method using metallic particles. One example of the former method is disclosed in JP-A 07-131135 and one example of the latter method is disclosed in JP-A 2003-315813.

However, the electroless plating method involves problems such as follows. Namely, in the case where a conductive pattern is formed on a substrate by means of the electroless plating method, the conductive pattern cannot be sufficiently adhered onto the substrate. Further, a plating layer formed by means of the electroless plating has a higher surface stress. For these reasons, when a conductive pattern is formed so as to have a larger thickness by means of this method, there is a problem in that such a conductive pattern is likely to be easily peeled off from the substrate.

In addition, there is another problem in that it is difficult to manufacture a conductive pattern having reliable quality because of the poor adhesion of the conductive pattern to the substrate.

On the other hand, the method using metallic particles involves such problems as follows. Namely, when a conductive pattern is formed using metallic particles, the metallic particles are supplied onto a substrate in the form of ink droplets, and thus there is a limit on the amount of the metallic particles to be contained in each ink droplet and its patterning preciousness. Therefore, there is a problem in that a gap is likely to be formed among the metallic particles, and thus when a conductive pattern having a relatively large area is formed, crack or breaking is likely to occur. Further, in this method, a binder is contained in the ink for holding the metallic particles in each ink droplet, and this makes it difficult to form a conductive pattern having low resistance.

SUMMARY

Accordingly, it is an object of the present invention to provide a method of forming a conductive pattern having superior conductivity and better adhesion with a substrate, thereby enabling a thick conductive pattern to be formed, a wiring substrate having a conductive pattern formed by the method, an electronic device having high reliability and electronic equipment provided with such an electronic device.

In order to achieve the above-mentioned object, the present invention is directed to a method of forming a predetermined conductive pattern on a substrate. The method comprises the steps of preparing a substrate, forming a metallic core containing metallic particles on the substrate by a droplet ejecting method so that the metallic core has a pattern substantially the same as the predetermined conductive pattern, and forming a plating layer so as to cover the surface of the metallic core by carrying out at least one electroless plating to thereby obtain the conductive pattern.

According to the conductive pattern forming method as described above, it is possible to form a conductive pattern having better adhesion with the substrate and having a relatively large thickness.

In the conductive pattern forming method according to the present invention, it is preferred that the average thickness of the metallic core is in the range of 1 to 1 to 10 μm.

According to the conductive pattern forming method as described above, it is possible to prevent the conductivity of a conductive pattern to be formed from being lowered even in the case where the metallic core contains a binder, and therefore the metallic core can exhibit sufficient function as a core of the plating layer.

Further, in the conductive pattern forming method according to the present invention, it is also preferred that the metallic particles are mainly formed of at least one material selected from the group comprising gold, silver, copper, nickel, palladium and an alloy containing at least one of these metals.

According to the conductive pattern forming method as described above, it is possible to improve the conductivity of a conductive pattern to be formed as a whole since these metallic particles have superior conductivity.

Furthermore, in the conductive pattern forming method according to the present invention, it is also preferred that prior to the formation of the plating layer a catalyst is applied onto the surface of the metallic core selectively.

According to the conductive pattern forming method as described above, it is possible to form the plating layer efficiently.

In the conductive pattern forming method according to the present invention, it is preferred that in the plating layer forming step the electroless plating is carried out two or more times, and prior to each electroless plating after the first electroless plating has been carried out a catalyst is applied selectively onto the surface of the plating layer which has been formed by the preceding electroless plating.

This also makes it possible to form the plating layer efficiently.

In the conductive pattern forming method according to the present invention, it is preferred that the catalyst is mainly constituted from a material selected from the group comprising palladium, platinum, rhodium, iridium and tin and alloys containing at least one of these metals.

These catalysts are preferably used since they can exhibit particularly high catalytic action.

Further, in the conductive pattern forming method according to the present invention, it is preferred that in the plating layer forming step the electroless plating is carried out two or more time, and in each of the electroless platings the same electroless plating solution is used.

This makes it possible to obtain a conductive pattern having better adhesion with the substrate.

Further, in the conductive pattern forming method according to the present invention, it is preferred that in the plating layer forming step the electroless plating is carried out two or more times, and in each of the electroless platings a different electroless plating solution is used.

This makes it possible to obtain a conductive pattern having superior characteristics.

Furthermore, in the conductive pattern forming method according to the present invention, it is preferred that the plating layer is mainly formed of a material selected from the group comprising nickel, silver, gold and copper.

This also makes it possible to obtain a conductive pattern having superior characteristics.

Moreover, in the conductive pattern forming method according to the present invention, it is preferred that the thickness of the plating layer formed by the fist electroless plating is in the range of 100 to 1000 nm.

According to the conductive pattern forming method described above, it is possible to prevent the metallic core from being peeled off from the substrate with suppressing stress from being increased, thereby enabling to obtain a conductive pattern having better adhesion with the substrate.

Moreover, in the conductive pattern forming method according to the present invention, it is preferred that the thickness of the second or subsequent plating layer is in the range of 1 to 10 μm.

This also makes it possible to obtain a conductive pattern having superior characteristics with sufficient strength.

Moreover, in the conductive pattern forming method according to the present invention, it is preferred that the method further comprises prior to the metallic core forming step a step for forming a primary layer for the metallic core onto the substrate. Such a primary layer can be formed for various purposes.

In this case, it is preferred that the primary layer is provided for enhancing the adhesion between the metallic core and the substrate.

This makes it possible to further enhance adhesion of the conductive pattern with the substrate, thereby enabling to prevent the conductive pattern from being peeled off from the substrate.

Further, in the conductive pattern forming method as described above, it is preferred that the primary layer is formed into an electrical insulating layer.

This makes it possible to prevent short-circuit from occurring between conductive patterns even in the case where the conductive patterns are formed in close proximity with each other. Further, this also makes it possible to use a substrate made of a metallic material, and thus various materials can be used for the substrate.

Further, in the conductive pattern forming method according to the present invention, it is preferred that the substrate is formed into a non-metallic substrate.

This makes it possible to form a conductive pattern onto the substrate with better adhesion thereto though electroless plating being employed.

Another aspect of the present invention is directed to a wiring substrate. The wiring substrate comprises a substrate, and a conductive pattern formed on the substrate using the conductive pattern forming method mentioned above.

This makes it possible to obtain a wiring substrate having high reliability.

Further, other aspect of the present invention is directed to a wiring substrate. The wiring substrate comprises a substrate, and a conductive pattern including a metallic core containing metallic particles and formed so as to have a predetermined pattern and at least one plating layer provided so as to cover the surface of the metallic core.

This also makes it possible to obtain a wiring substrate having high reliability.

The other aspect of the present invention is directed to an electronic device provided with the wiring substrate mentioned above.

This makes it possible to provide an electronic device having high reliability.

Yet other aspect of the present invention is directed to electronic equipment provided with the electronic device mentioned above.

This also makes it possible to provide electronic equipment having high reliability.

These and other objects, structures and advantages of the present invention will be apparent from the following detailed description of the invention and the examples thereof which proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a part of a wiring substrate according to the present invention.

FIG. 2(a) to FIG. 2(g) are illustrations which show steps for forming a conductive pattern according to a fist embodiment of the present invention.

FIG. 3(a) to FIG. 3(c) are illustrations which show steps for forming a conductive pattern according to a second embodiment of the present invention.

FIG. 4 is an exploded perspective view which shows a case where an electronic device of the present invention is applied to a plasma display apparatus.

FIG. 5 is a perspective view which shows the structure of a personal mobile computer (or a personal notebook computer) to which the electronic equipment according to the present invention is applied.

FIG. 6 is a perspective view which shows the structure of a mobile phone (including the personal handyphone system (PHS)) to which the electronic equipment according to the present invention is applied.

FIG. 7 is a perspective view which shows the structure of a digital still camera to which the electronic equipment according to the present invention is applied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinbelow, a method of forming a predetermined conductive pattern, a wiring substrate, an electronic device and electronic equipment according to the present invention will be described in detail with reference to preferred embodiments shown in the accompanying drawings.

Method of forming a conductive pattern

First, a description will be made with regard to the method of forming a conductive pattern according to the present invention.

FIG. 1 is a perspective view of a part of a wiring substrate according to the present invention. As shown in FIG. 1, the conductive pattern forming method of the present invention is a method of forming a conductive pattern 3 which includes a metallic core 31 arranged in a predetermined pattern and containing metallic particles 31a, and a plating layer 32 provided so as to cover the metallic core 31.

First Embodiment

Hereinbelow, a description will be made with regard to the first embodiment of the conductive pattern forming method according to the present invention.

FIG. 2(a) to FIG. 2(g) are illustrations which show steps for forming a conductive pattern according to the fist embodiment of the present invention. In the following description, an upper side in FIGS. 2(a) to FIG. 2(g) is referred to as “upper” or “top” and a lower side in these figures is referred to as “lower” or “bottom”.

The conductive pattern forming method shown in FIG. 2(a) to FIG. 2(g) include a metallic core formation step (1A) and a plating layer formation step (2A). Hereinbelow, these steps will be explained in this order.

First, as shown in FIG. 2(A), a substrate 2 on which a conductive pattern 3 is to be formed is prepared. As for the substrate 2, various types of substrates can be used. Examples of such substrates include non-metallic substrates such as silicon wafer, silica glass substrate, and plastic film, and metallic substrates. Further, these substrates may be used in a state that an additional film or layer such as a semiconductor film, a metallic layer, a dielectric layer, or an organic layer is formed on the surface thereof.

Among these substrates mentioned above, non-metallic substrates are preferably used for the substrate 2. According to the conductive pattern forming method of the present invention, it is possible to form a conductive pattern 3 onto a non-metallic substrate 2 with better adhesion thereto though electroless plating being employed.

(1A) Metallic Core Formation Step

First, as shown in FIG. 2(b), a metallic core forming material 310 containing metallic particles 31 a is ejected onto the substrate 2 using a droplet ejecting method such as an ink-jet method for instance to form a metallic core 31 as shown in FIG. 2(c).

At this time, the metallic core 31 is formed so that the metallic core 31 has a pattern substantially the same as a predetermined conductive pattern 3 to be formed. By using the droplet ejecting method, it is possible to form the metallic core 31 having such a pattern easily with better dimensional precision without using a resist layer (mask).

The metallic core 31 functions not only as a core from which a plating layer 32 described later grows but also as a joining layer for joining the substrate 2 and the plating layer 32.

As for the metallic particles 31 a, silver, gold, copper, nickel, palladium, platinum and an alloy containing one or more of these metals may be used. In particular, it is preferred that the metallic particles 31 a are formed from a metallic material containing at least one of silver, gold, copper, nickel, palladium, platinum and an alloy containing one or more of these metals as its main material. Since such metallic particles 31 a have a superior conductivity, use of such metallic particles 31 a makes it possible to improve conductivity of a conductive pattern to be formed as a whole.

These metallic particles 31 a may be used with an organic coating or the like for improving dispersibility thereof in a metallic core forming material 310.

The average particle size of the metallic particles 31 a is not particularly limited to a specific value, but preferably in the range of 1 to 100 nm, and more preferably in the range of 1 to 50 nm. If the particle size of the metallic particles 31 a is too small, aggregation of the metallic particles 31 a are likely to occur, and thus there is a possibility that dispersibility of the metallic core forming material 310 is lowered. On the other hand, if the particle size of the metallic particles 31 a is too large, there is a possibility of clogging of a nozzle of a droplet ejecting head.

As for a dispersant which is used for preparing the metallic core forming material 310 (in which the metallic particles 31 a are to be dispersed), it is preferred, but not limited thereto, that its vapor pressure at room temperature is in the range of 0.001 to 200 mmHg (about 0.133 to 26600 Pa), and more preferably in the range of 0.001 to 50 mmHg (about 0.133 to 6650 Pc). If the vapor pressure of the dispersant is too low, vaporization of the dispersant becomes insufficient, which shows a tendency that the dispersant is likely to remain in the metallic core 31 and thus this is not desirable. On the other hand, if the vapor pressure is too high, the dispersant is abruptly vaporized after the metallic core forming material 310 has been ejected onto the substrate 2, and thus there is a possibility that it becomes difficult to form a desired metallic core 31. Further, since nozzle clogging becomes likely to occur due to drying when the metallic core forming material 310 is ejected by means of the droplet ejecting method in the form of droplets, there is a case that stable droplet ejection cannot be carried out.

Examples of such a dispersant include, but not limited. thereto, in addition to water, alcohols such as methanol, ethanol, propanol, and butanol; hydrocarbons such as n-heptane, n-octane, decane, tetradecane, toluene, xylene, cymene, durene, indene, dipentene, tetrahydronaphthalene, decanaphthalene, and cyclohexylbenzene; ethers such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, 1,2-dimethoxy ethane, bis(2-methoxyethyl)ether, and p-dioxiane; propylene carbonate; γ-butyrolactone; N-methyl-2-pyrrolidone; dimethylformamide; dimethylsulfoxide; and cyclohexanone; and the like.

Among these dispersants, water, alcohols, hydrocarbons, and ethers are preferably used, and in particular water and hydrocarbons are more preferably used. These dispersants can easily disperse metallic particles 31 a uniformly. Further, the metallic core formation material 310 prepared using these dispersants has superior preservation stability, and thus it is suitable for the droplet ejecting method.

Further, the content of the metallic particles 31 a in the metallic core formation material 410 (that is, concentration of dispersoid) may be changed appropriately so as to meet with the thickness of a metallic core 31 to be formed, but preferably it is set to 1 to 80 wt % and more preferably to 10 to 60 wt %.

In this connection, it is to be noted that if the content of the metallic particles 31 a is larger than the upper limit value, aggregation of the metallic particles 31 a is likely to occur and thereby it becomes difficult to obtain a metallic core 31 having a uniform thickness.

The surface tension of the metallic core formation material 310 is preferably in the range of 0.02 to 0.07 N/m, and more preferably in the range of 0.02 to 0.05 N/m. If the surface tension is too low when the metallic core formation material 310 is ejected by the droplet ejecting method, wettability of the metallic core formation material 310 of the nozzle surface increases, thereby leading to a possibility that indirectional ejection is likely to occur. On the other hand, if the surface tension is too high, a form of meniscus at the tip of the nozzle is not stable, thereby leading to a possibility that it becomes difficult to control an amount of ejection as well as a timing of ejection.

In order to adjust the surface tension of the metallic core formation material 310, the metallic core formation material 310 may contain minute amounts of a surface tension adjustment agent to such an extent that contact angle to the substrate 2 is not decreased over the necessary angle. Examples of such surface tension adjustment agent include a fluorine-based surface tension adjustment agent, a silicone-based surface tension adjustment agent, and a nonionic surface tension adjustment agent. For example, when a nonionic surface tension adjustment agent is added, the wettability of the metallic core formation material 310 to the substrate 2 is improved and thereby a leveling property of the metallic core 31 to be formed is also improved. This makes it possible to prevent fine irregularities are to be formed on the metallic core 31.

The metallic core formation material 310 may further contain organic compounds such as alcohol, ether, ester, ketone, and the like, as needed.

The viscosity of the metallic core formation material 310 is preferably in the range of 1 to 50 mPa·s, and more preferably in the range of 5 to 50 mPa·s. If the viscosity of the metallic core formation material 310 is too low when it is ejected by the droplet ejecting method, the periphery of the nozzle is apt to be contaminated due to leakage of the metallic core formation material 310. On the other hand, if the viscosity of the metallic core formation material 310 is too high, clogging of the nozzle is likely to occur, which makes it difficult to smoothly eject the metallic core formation material 310.

The metallic core formation material 310 which has been supplied onto the substrate 2 so as to have a predetermined pattern may be subjected to heat treatment as needed, thereby forming the metallic core 31. When the metallic core 31 contains a binder, the binder present in the vicinity of the surface thereof can be removed by this heat treatment to thereby expose the metallic particles 31 a.

The thickness of the metallic core 31 to be formed is not particularly limited to a specific value, but preferably in the range of 1 to 10 μm, and more preferably in the range of 1 to 5 μm. If the thickness of the metallic core 31 is too thin, there is a case that the metallic core 31 does not function properly as a core of a plating layer 32 described later. On the other hand, if the thickness of the metallic core 31 is too thick over the upper limit value mentioned above, there is a possibility that the conductivity of a conductive pattern 3 to be formed is extremely reduced. Such a situation occurs, for example, in the case where the metallic core 31 contains a binder and depending on the kind and/or amount of the binder.

[2A] Plating Layer Formation Step

Next, electroless plating is carried out at least one time (in this embodiment, four times) to form a plating layer 32 so as to cover the surface of the metallic core 31, thereby obtaining a conductive pattern 3.

Specifically, first, as shown in FIG. 2(d), a catalyst 5 is applied onto the surface of the metallic core 31 selectively. This makes it possible to form a first layer 321 (plating layer 32) efficiently.

The application of the catalyst 5 is carried out by applying (supplying) a catalyst application liquid containing the catalyst 5 to the surface of the metallic core 31.

As for the method for applying the catalyst application liquid to the surface of the metallic core 31, various application methods can be used. Examples of such application methods include a dip coating method, a spin coating method, a slit coating method, a cap coating method, a dispenser method, a spray coating method, a roll coating method, and an ink-jet method (droplet ejecting method). Among these methods, any one or a combination of any two or more of the methods can be used.

Examples of the catalyst 5 include palladium, platinum, rhodium, iridium and tin-palladium mixture solution and alloys containing at least one of these metals. Among them, a catalyst containing at least one of palladium, platinum, tin-palladium mixture solution and an alloy containing at least one of them at its main material is particularly preferable, since such a catalyst 5 exhibits an especially high catalytic action.

The catalyst application liquid can be adjusted, for example, by dissolving a salt of the catalyst (halide or the like) in a solvent.

When such a catalyst application liquid is applied to the surface of the metallic core 31 so as to be in contact with the surface, the catalyst 5 is participated onto the surface of the metallic particles 31 a in the form of the simple substance of the metal.

Therefore, it is preferred that the surface of the metallic core 31 is subjected to activation treatment prior to the application of the catalyst application liquid to the surface of the metallic core 31. As for an example of such activation treatment, treatment for removing a coating agent or an oxidized film on the surfaces of the metallic particles 31 a, that is a light etching can be mentioned. This makes it possible to participate (attach) the catalyst onto the surfaces of the metallic particles 31 a more reliably.

The amount of the removal of the surfaces of the metallic particles 31 a by the light etching can be adjusted by setting the concentration of the etchant and etch time and the like.

Further, any specific limitations are imposed on the conditions when the catalyst is applied to the surface of the metallic core 31 such as a concentration of the salt in the catalyst application liquid, a temperature of the catalyst application liquid, and a contacting time of the catalyst application liquid onto the surface of the metallic core 31.

In this regard, it is to be noted that in the case where the metallic particles 31 a in the metallic core 31 exhibit catalytic action, the application of the catalyst onto the surface of the metallic core 31 can be omitted.

Next, a first time electroless plating is carried out by immersing the substrate 2 on which the metallic core 31 has been formed into an electroless plating solution. As a result, as shown in FIG. 2(e), a first layer 321 is formed on the surface of the metallic core 31 with the catalyst 5 being used as a core.

In this step, the average thickness of the first layer 321 is not particularly limited to a specific value, but preferably in the range of 100 to 1000 nm, and more preferably in the range of 150 to 800 nm. If the average thickness of the first layer 321 is less than the lower limit value, there is a possibility that the formed metallic core still remains in an island state that does not form a core sufficiently, and as a result, there is a case that the metallic core formed has uneven properties. On the other hand, if the average thickness of the first layer 321 exceeds the above upper limit value, there is a case that the formed metallic core 31 is likely to be peeled off from the substrate 2.

The thickness of the first layer 321 can be adjusted or controlled, for example, by setting appropriately the concentration of the metallic salt in the electroless plating solution, the temperature of the electroless plating solution, and the immersing time of the substrate 2 into the electroless plating solution, and the like.

Next, after a catalyst is applied to the surface of the first layer 321 in the same manner as the previous step, a second layer 322 is formed as shown in FIG. 2(f) by immersing the substrate 2 into the electroless plating solution, that is, by carrying out a second electroless plating.

By carrying out the electroless plating repeatedly as described above, a third layer 323 and then a fourth layer 324 are sequentially formed as shown in FIG. 2(g). In this way, the plating layer 32 is obtained.

As described above, by forming the plating layer 32 by means of a plurality of electroless platings, it is possible to obtain a plating layer 32 having a large thickness with maintaining better adhesion to the metallic core 31 reliably.

In the process of forming the plating layer 32 described above, the thickness of each layer formed by each electroless plating may be substantially the same as with each other, but it is preferred that the thickness of each layer is different from each other, in particular, that the newly formed plating layer has a lager thickness. This makes it possible to obtain a conductive pattern 3 having more better adhesion to the substrate 2.

Further, in this case, the same electroless plating solution may be used for each of the electroless platings, or a different electroless plating solution may be used for at least one time for the electroless platings.

In the case where the same electroless plating solution is used for each of the electroless platings, there is an advantage in that it is possible to obtain better adhesion between the adjacent plating layers without taking any consideration to the compatibility between the adjacent layers.

On the other hand, in the case where a different electroless plating solution is used for at least one time for the electroless platings, there are advantages such as follows.

(1) For example, in the case where a gold electroless plating solution is used as an electroless plating solution for the final electroless plating so that the surface and its vicinity of the conductive pattern 3 is constituted of gold, it becomes possible not only to protect the conductive pattern 3 but also to carry out connection with other patterns or wirings easily.

(2) For example, in the case where the plating layer is constituted from a laminate structure including a nickel plating layer and a gold or silver plating layer, it becomes possible to reduce manufacturing costs with maintaining the conductivity, since nickel is relatively inexpensive.

(3) For example, in the case where by laminating layers having surface stresses exerting in the mutually opposite directions, it becomes possible to cancel or relive the surface stresses in the plating layer 32, thereby enabling to prevent the plating layer 32 from being peeled off from the substrate 2 reliably. In this regard, it is to be noted that in general examples of a layer in which surface stress appears in a compression direction positively include a nickel-phosphorus plating layer, and examples of a layer in which surface stress appears in a tensile direction positively include a nickel-boron plating layer and a copper plating layer.

In the above embodiment, the times of electroless plating are not limited to four times, and the electroless plating may be carried out for one, two, three, five or more times.

The average thickness of the plating layer 32 is not particularly limited to a specific value, but preferably in the range of 1 to 10 μm, and more preferably in the range of 1 to 5 μm. This makes it possible to obtain a conductive pattern 3 having higher conductivity.

Further, as for the constituent material for the plating layer 32, silver can be mentioned in addition to nickel, copper and gold mentioned above, and one of these materials or a combination (laminate) of tow or more of these materials are preferably used. These materials are particularly preferable in their superior conductivity as a conductive pattern.

By ways of the above-mentioned steps, a wiring substrate 1 of the present invention is manufactured. Since in such a wiring substrate 1 the conductive pattern 3 has higher conductivity and it is provided on the substrate 2 with better adhesion thereto so as not to be easily peeled off therefrom, the wiring substrate 1 can have high reliability.

Second Embodiment

Next, a description will be made with regard to a second embodiment of the conductive pattern forming method according to the present invention.

FIG. 3(a) to FIG. 3(c) are illustrations which show steps for forming a conductive pattern according to a second embodiment of the present invention. In the following description, an upper side in FIGS. 3(a) to FIG. 3(c) is referred to as “upper” or “top” and a lower side in these figures is referred to as “lower” or “bottom”.

The following description concerning the conductive pattern forming method according to the second embodiment of the present invention will focus on the difference from the conductive pattern forming method of the first embodiment, and the common descriptions will be omitted.

Namely, the second embodiment is the same as the first embodiment excepting that a primary layer 4 is formed prior to the formation of the metallic core 31. The conductive pattern formation method shown in FIG. 3(a) to FIG. 3(c) is comprised of a primary layer formation step (1B), a metallic core formation step (2B) and a plating layer formation step (3B).

(1B) Primary Layer Formation Step

First, as shown in FIG. 3(a), a primary layer 4 is formed on a substrate 2. The primary layer 4 is provided for enhancing adhesion between the metallic core 31 and the substrate 2. Since the adhesion between the metallic core 31 and the substrate 2 is enhanced by providing such a primary layer 4, it is possible to prevent the metallic core 31 (that is, the conductive pattern 3) from being peeled off from the substrate 2 even in the case where the substrate 2 has flexibility.

In this regard, it is preferred that the primary layer 4 is insulative. This makes it possible to prevent short-circuit from occurring between conductive patterns 3 even in the case where the conductive patterns 3 are formed in close proximity with each other. Further, this also makes it possible to use a substrate 2 made of a metallic material, and thus various materials can be selectively used for the substrate 2.

Examples of such a primary layer 4 include polyolefin such as polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinylacetate copolymer (EVA); cyclic polyolefin; modified polyolefin; polyvinyl chloride; polyvinylidene chloride; polystyrene; polyamide; polyimide; polyamide-imide; polycarbonate; poly-(4-methylpentene-1); ionomer; acrylic resin; polymethyl methacrylate; acrylonitrile-butadiene-styrene copolymer (ABS resin); acrylonitrile-styrene copolymer (AS resin); butadiene-styrene copolymer; polyoxymethylene; polyvinyl alcohol (PVA); ethylene-vinylalcohol copolymer (EVOH); polyester such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycyclohexane terephthalate (PCT)); polyether; polyether ketone (PEK); polyether ether ketone (PEEK); polyetherimide; polyacetal (POM); polyphenylene oxide; modified polyphenylene oxide; polysulfone; polyethersulfone; polyphenylene sulfide; polyalylate; aromatic polyester (liquid crystalline polymer); fluoro-based resin such as polytetrafluoroethylene, and polyvinylidene fluoride; various thermoplastic elastomers such as polystyrene based elastomer, polyolefin based elastomer, polyvinylchloride-based elastomer, polyurethane-based elastomer, polyester-based elastomer, polyamide-based elastomer, polybutadiene-based elastomer, transpolyisoprene-based elastomer, fluororubber-based elastomer, chlorinated polyethylene-based elastomer and the like; epoxy resin; phenol resin; urea resin; melamine resin; unsaturated polyester; silicone resin; polyurethane resin; and copolymer, blended body or polymer alloy each having at least one of these materials mentioned above as a main ingredient. In this case, one kind of these materials or a mixture of two or more kinds of these materials (in the form of a laminate comprised of two ore more layers) may be employed.

The average thickness of the primary layer 4 is not particularly limited to a specific value, but preferably in the range of 1 to 25 μm, and more preferably in the range of 5 to 20 μm. If the thickness of the primary layer 4 is too small, there are cases, depending on the constituent material of the primary layer 4, that sufficient adhesion cannot be obtained between the substrate 2 and the metallic core 31 and that sufficient insulation cannot be exhibited. On the other hand, if the thickness of the primary layer exceeds the above mentioned upper limit value, not only further effect cannot be expected but also flexibility of the substrate 2 is lowered in the case where the substrate 2 has flexibility.

Further, the primary layer 4 may be formed by applying a primary layer formation material in which such a material as mentioned above or its precursor is dissolved or dispersed onto the substrate 2 and then subjecting such a substrate 2 to drying, heat treatment, or irradiation of ultraviolet rays, or the like.

As for the method for applying the primary layer formation material onto the substrate 2, various methods which are the same as those mentioned with reference to the method for applying the catalyst applying liquid described above may be employed.

The primary layer 4 may be provided for the purpose of achieving an object other that the object for enhancing the adhesion between the metallic core 31 and the substrate 2, and for achieving both the objects.

Further, in the example shown in the drawing, the primary layer 4 is formed onto the entire surface of the substrate 2. However, the present invention is not limited to such a structure, and it is possible to form a primary layer 4 so as to have a pattern similar to a conductive pattern 3 to be formed.

(2B) Metallic Core Formation Step

This step is carried out in the same manner as the above-mentioned step (1A). Through this step, a metallic core 31 is formed on the primary layer 4.

(3B) Plating Layer Formation Step

This step is carried out in the same manner as the above-mentioned step (2A). Through this step, a plating layer 4 is formed so as to cover the surface of the metallic core 31.

Through the steps mentioned above, a wiring substrate of the present invention can be obtained.

In this second embodiment, since the primary layer 4 is formed on the substrate 2, adhesion of the conductive pattern 3 to the substrate 2 is enhanced, thereby enabling to prevent the conductive pattern 3 from being peeled off from the substrate 2 reliably.

Electronic Device

The wiring substrate 1 described above can be applied to various electronic devices such as semiconductor devices and displays (e.g. liquid crystal displays, organic EL devices, and plasma displays and the like).

In the following, a description will be made based on an example case where the electronic device of the present invention is applied to a plasma display.

FIG. 4 is an exploded perspective view which shows a case where an electronic device of the present invention is applied to a plasma display apparatus.

The plasma display device 500 shown in FIG. 4 is generally composed from a glass substrates 501 and a grass substrate 502 which are arranged so as to oppose to each other, and a discharge and display section provided between the glass substrates 501, 502.

The discharge and display section 510 includes a plurality of discharge cells 516. In these discharge cells 516, three discharge cells comprised of a red discharge cell 516(R), a green discharge cell 516(G) and a blue discharge cell 516(B) form a unit which functions as a pixel.

On the upper surface of the glass substrate 501, there are formed address electrodes 511 which are arranged in a strip manner with a predetermined interval, and a dielectric layer 519 is formed on the address electrodes 511 and the grass substrate 501 so as to cover the upper surfaces thereof.

Further, one the dielectric layer 519, partitioning walls 515 are formed so as to be positioned between the adjacent address electrodes 511, 511 and extended along each address electrode 511.

At predetermined positions of the partitioning walls 515 in the longitudinal direction thereof, additional partitioning walls (not shown in the drawing) are also provided so as to extend in a direction perpendicular to each address electrode 511. As a result, there are formed rectangular regions each defined by a pair of partitioning walls arranged at both sides of each address electrode 511 and a pair of partitioning walls arranged in a predetermined interval so as to extend in a direction perpendicular to the address electrode 511, and the discharge cells 516 are formed so as to correspond to the rectangular regions, respectively. A unit comprised of three of these rectangular regions constitutes the pixel.

Further, inside each of the rectangular regions defined by the partitioning walls 515, there is provided a fluorescent layer 517. The fluorescent layer 517 emits fluorescence having a color of any one of red, green and blue. In more details, a red fluorescent layer 517(R) is provided on the bottom of the red discharge cell 516(R), a green fluorescent layer 517(G) is provided on the bottom of the green discharge cell 516(R), and a blue fluorescent layer 517(B) is provided on the bottom of the blue discharge cell 516(B).

On the other hand, on the glass substrate 502, a plurality of transparent display electrodes 512 are formed in a stripe manner with a predetermined interval along a direction perpendicular to the address electrode 511. These transparent display electrodes 512 are formed of a transparent conductive material such as ITO, FTO and ATO and the like. Further, metallic bus electrodes 512 a are formed in contact with the transparent display electrodes 512, respectively. These bus electrodes 512 a have a function of decreasing a resistance value of the transparent display electrode 512.

Further, on the transparent display electrodes 512 and the bus electrodes 512 a, a dielectric layer 513 are formed so as to cover these electrodes 512, 512 a, and one the dielectric layer 513, there is formed a protective layer 514 formed of MgO or the like.

The glass substrate 501 having the above structure is stuck onto the glass substrate 502 together so that the address electrodes 511 are orthogonal to the transparent display electrodes 512, and then the spaces defined by the fluorescent layers 517 and the protective layer 513 are evacuated and in turn rare gas is charged therein to form the discharge cells 516.

In this regard, it is to be noted that the transparent display electrodes 512 are formed on the glass substrate 502 so that two electrodes 512 are allotted to each discharge cell 516.

The address electrodes 511 and the transparent display electrodes 512 are connected to an AC power source not shown in the drawing. By supplying electrical current to predetermined electrodes, the fluorescent layers 517 at the corresponding discharge display section are excited to emit a light, thereby enabling to provide color display.

In such a plasma display 500, the glass substrate 501 on which the address electrodes 511 are formed can be formed from a wiring substrate according to the present invention.

Electronic Equipment

The electronic device of the present invention may be applied to various types of electronic equipment.

FIG. 5 is a perspective view which shows the structure of a personal mobile computer (or a personal notebook computer) to which the electronic equipment according to the present invention is applied.

In FIG. 5, a personal computer 1100 is comprised of a main body 1104 provided with a keyboard 1102 and a display unit 1106 provided with a display. The display unit 1106 is rotatably supported by the main body 1104 via a hinge structure.

In the personal computer 1100, for example, the display unit 1106 includes the display (electronic device) described above.

FIG. 6 is a perspective view which shows the structure of a mobile phone (including the personal handyphone system (PHS)) to which the electronic equipment according to the present invention is applied.

The mobile phone 1200 includes a plurality of operation buttons 1202, an ear piece 1204, a mouthpiece 1206, and a display section provided with the display (electronic device) described above.

FIG. 7 is a perspective view which shows the structure of a digital still camera to which the electronic equipment according to the present invention is applied. In this drawing, interfacing to external devices is simply illustrated.

In a conventional camera, a silver salt film is exposed to the optical image of an object. On the other hand, in the digital still camera 1300, an image pickup device such as a CCD (Charge Coupled Device) generates an image pickup signal (or an image signal) by photoelectric conversion of the optical image of an object.

In the rear surface of a case (or a body) 1302 of the digital still camera 1300, there is provided a display which provides an image based on the image pickup signal generated by the CCD. That is, the display functions as a finder which displays the object as an electronic image.

Inside the case, there is provided a circuit board 1308. The circuit board 1308 has a memory capable of storing an image pickup signal.

On the front surface of the case 1302 (in FIG. 7, the front surface of the case 1302 is on the back side), there is provided a light receiving unit 1304 including an optical lens (an image pickup optical system) and a CCD.

When a photographer presses a shutter button 1306 after checking an object image on the display, an image pickup signal generated by the CCD at that time is transferred to the memory in the circuit board 1308 and then stored therein.

Further, on the side surface of the case 1302 of the digital still camera 1300, there are provided a video signal output terminal 1312 and an input-output terminal for data communication 1314. As shown in FIG. 7, when necessary, a television monitor 1430 and a personal computer 1440 are connected to the video signal output terminal 1312 and the input-output terminal for data communication 1314, respectively. In this case, an image pickup signal stored in the memory of the circuit board 1308 is outputted to the television monitor 1430 or the personal computer 1440 by carrying out predetermined operation.

The electronic equipment according to the present invention can be applied not only to the personal computer (which is a personal mobile computer) shown in FIG. 5, the mobile phone shown in FIG. 6, and the digital still camera shown in FIG. 7 but also to other electronic equipment. Examples of such other electronic equipment include a television set, a video camera, a view-finder or monitor type of video tape recorder, a laptop-type personal computer, a car navigation device, a pager, an electronic notepad (which may have communication facility), an electronic dictionary, an electronic calculator, a computerized game machine, a word processor, a workstation, a videophone, a security television monitor, an electronic binocular, a POS terminal, an apparatus provided with a touch panel (e.g., a cash dispenser located on a financial institute, a ticket vending machine), medical equipment (e.g., an electronic thermometer, a sphygmomanometer, a blood glucose meter, an electrocardiograph monitor, ultrasonic diagnostic equipment, an endoscope monitor), a fish detector, various measuring instruments, gages (e.g., gages for vehicles, aircraft, and boats and ships), a flight simulator, various monitors, and a projection display such as a projector.

In the foregoing, the conductive pattern forming method, the wiring substrate, the electronic device and the electronic equipment according to the present invention have been described based on the embodiments shown in the drawings, but the present invention is not limited thereto.

For example, in the conductive pattern forming method according to the present invention, one or more arbitrary steps may be added. Further, in the electronic device and the electronic equipment of the present invention, some components may be replaced with other components which have the same functions, and some other arbitrary components or elements may be added thereto.

EXAMPLES

Hereinbelow, practical examples of the present invention will be described.

1. Manufacture of Wiring Substrate

Example 1

At first, a metallic core formation material was prepared. As for the metallic core formation material, a solution in which silver particles having the average particle size of about 5 nm are dispersed in an organic solvent (“PERFECT SILVER”, product of ULVAC Materials, Inc.) was prepared, but its dispersant, that is the organic solvent was changed to tetradecane.

In the above metallic core formation material, the amount of the silver particles was 60 wt % and the viscosity was 8 mPa·s, and the surface tension was 0.05 N/m.

The metallic core formation material was ejected onto a glass substrate using an ink-jet printer head manufactured by SEIKO EPSON Corporation so as to draw a pattern as shown in FIG. 1. In this regard, it is to be noted that the ink-jet printer head was obtained by modifying an ink-jet printer head of a printer PM950C (manufactured and sold by SEIKO EPSON Corporation) so as to be able to stand for organic solvents.

Next, the metallic core formation material ejected onto the glass substrate so as to have the predetermined pattern was dried at room temperature for two hours, and then it was calcined in a nitrogen atmosphere at a temperature of 400° C. for one hour.

The thus obtained metallic core was comprised of a thin wire section having an average thickness of 3 μm and an average width of 20 μm and a pad section having an average thickness of 3 μm and an area (at a flat portion) of 0.15 mm².

Next, the metallic core was subjected to a light etching.

Next, the glass substrate on which the metallic core was formed was immersed into a catalyst application liquid containing palladium salt (“ACTIVATOR”, product of Meltec Ltd.) for one minute, thereby applying palladium (catalyst) onto the surface of the metallic core.

Next, the glass substrate was removed from the catalyst application liquid and then it was washed. Thereafter, the glass substrate was immersed into a nickel plating solution (“Electroless nickel plating solution”, product of Meltec Ltd.) for two minutes, thereby carrying out nickel plating onto the metallic core to form a nickel layer having an average thickness of 160 nm so as to cover the surface of the metallic core.

Next, the glass substrate was washed with water and then it was immersed into the same catalyst application liquid for two minutes, and after the glass substrate was washed with water, the glass substrate was immersed into the same nickel plating solution for three minutes.

Next, the above process was repeated for three times with changing the immersion time into the nickel plating solution to three minutes, five minutes and five minutes, respectively.

Finally, a displacement gold plating was carried out to thereby forming a plating layer to obtain a conductive pattern.

It was confirmed that the thus obtained conductive pattern had an average thickness of 8 μm (an average thickness of the plating layer was 5 μm), and the surfaces of both the thin wire section and the pad section were dense surfaces.

Example 2

A conductive pattern was formed in the same manner as in the Example 1 excepting that a polyimide film was used as a substrate and the conductive pattern was formed on the polyimide film fixed on the glass substrate.

In this example, the process of electroless plating was same as that of the Example 1, but the nickel plating was carried out for three times. Further, the immersion times into the nickel plating solution were one minutes, three minutes and seven minutes, respectively.

It was confirmed that the thus obtained conductive pattern had an average thickness of 6 μm (an average thickness of the plating layer was 5 μm), and the surfaces of both the thin wire section and the pad section were dense surfaces.

Example 3

A wiring substrate was formed in the same manner as in the Example 1 excepting that a primary layer formed as mentioned below was provided.

A precursor of an epoxy resin was applied onto a glass substrate by a spin coating method, and it was calcined at a temperature of 280° C. for one hour, to thereby form the primary layer having an average thickness of 5 μm.

Example 4

A wiring substrate was formed in the same manner as in the Example 2 excepting that a primary layer was provided in the same manner as the Example 3.

Comparative Example 1

A wiring substrate was manufactured in the same manner as in the Example 1 excepting that the metallic core was omitted.

Comparative Example 2

A wiring substrate was manufactured in the same manner as in the Example 2 excepting that the metallic core was omitted.

Comparative Example 3

A wiring substrate was manufactured in the same manner as in the Example 3 excepting that the metallic core was omitted.

Comparative Example 4

A wiring substrate was manufactured in the same manner as in the Example 4 excepting that the metallic core was omitted.

2. Evaluation

A tape peel test was carried out for each of the wiring substrates obtained in the Examples and the Comparative Examples. This test was carried out in accordance with (a) Tape test method of (8) Peeling test method in the test methods determined by JIS H 8504 (Test method for adhesion of plating).

As a result of the tests mentioned above, it was confirmed that in the wiring substrate manufactured in each of the Examples no peeling-off of the conductive pattern from the substrate was observed and thus there was no problem.

On the other hand, in the wiring substrate of each of the Comparative Examples, peeling-off of the conductive pattern from the substrate was observed with naked eyes.

Further, it was also confirmed that in the wiring substrate manufactured in each of the Examples there was no problem in the electrical characteristics of the conductive pattern.

Finally, it is to be understood that the present invention is not limited to the Examples described above, and many changes or additions may be made without departing from the scope of the invention which is determined by the following claims. 

1. A method of forming a predetermined conductive pattern on a substrate, comprising the steps of: preparing a substrate; forming a metallic core containing metallic particles on the substrate by a droplet ejecting method so that the metallic core has a pattern substantially the same as the predetermined conductive pattern; and forming a plating layer so as to cover the surface of the metallic core by carrying out at least one electroless plating to thereby obtain the conductive pattern.
 2. The method for forming a predetermined conductive pattern as claimed in claim 1, wherein the average thickness of the metallic core is in the range of 1 to 1 to 10 μm.
 3. The method for forming a predetermined conductive pattern as claimed in claim 1, wherein the metallic particles are mainly formed of at least one material selected from the group comprising gold, silver, copper, nickel, palladium and an alloy containing at least one of these metals.
 4. The method for forming a predetermined conductive pattern as claimed in claim 1, wherein prior to the formation of the plating layer a catalyst is applied onto the surface of the metallic core selectively.
 5. The method for forming a predetermined conductive pattern as claimed in claim 1, wherein in the plating layer forming step the electroless plating is carried out two or more times, and prior to each electroless plating after the first electroless plating has been carried out a catalyst is applied selectively onto the surface of the plating layer which has been formed by the preceding electroless plating.
 6. The method for forming a predetermined conductive pattern as claimed in claim 4, wherein the catalyst is mainly constituted from a material selected from the group comprising palladium, platinum, rhodium, iridium and tin and alloys containing at least one of these metals.
 7. The method for forming a predetermined conductive pattern as claimed in claim 1, wherein in the plating layer forming step the electroless plating is carried out two or more times, and in each of the electroless platings the same electroless plating solution is used.
 8. The method for forming a predetermined conductive pattern as claimed in claim 1, wherein in the plating layer forming step the electroless plating is carried out two or more times, and in each of the electroless platings a different electroless plating solution is used.
 9. The method for forming a predetermined conductive pattern as claimed in claim 1, wherein the plating layer is mainly formed of a material selected from the group comprising nickel, silver, gold and copper.
 10. The method for forming a predetermined conductive pattern as claimed in claim 5, wherein the thickness of the plating layer formed by the fist electroless plating is in the range of 100 to 1000 nm.
 11. The method for forming a predetermined conductive pattern as claimed in claim 1, wherein the thickness of the second or subsequent plating layer is in the range of 1 to 10 μm.
 12. The method for forming a predetermined conductive pattern as claimed in claim 1, further comprising prior to the metallic core forming step a step for forming a primary layer for the metallic core onto the substrate.
 13. The method for forming a predetermined conductive pattern as claimed in claim 12, wherein the primary layer is provided for enhancing the adhesiveness between the metallic core and the substrate.
 14. The method for forming a predetermined conductive pattern as claimed in claim 12, wherein the primary layer is formed into an electrical insulating layer.
 15. The method for forming a predetermined conductive pattern as claimed in claim 1, wherein the substrate is formed into a non-metallic substrate.
 16. A wiring substrate, comprising: a substrate; and a conductive pattern formed on the substrate using the conductive pattern forming method defined in claim
 1. 17. A wiring substrate, comprising: a substrate; and a conductive pattern including a metallic core containing metallic particles and formed so as to have a predetermined pattern and at least one plating layer provided so as to cover the surface of the metallic core.
 18. An electronic device provided with the wiring substrate defined in claimed
 16. 19. Electronic equipment provided with the electronic device defined in claim
 18. 